An engine of a vehicle may be automatically stopped and restarted during periods of time when vehicle motion is not requested or desired by the vehicle operator. By stopping the engine, it may be possible to conserve fuel that would otherwise be consumed if the engine were allowed to continue to operate. However, restarting the engine can increase engine emissions if an undesirable amount of fuel is inducted to engine cylinders. Further, where the engine is a port fueled engine, it may be more difficult to control fuel amounts entering engine cylinders since fuel can only enter the cylinders during times when intake valves of the cylinders are open. Consequently, it may take longer to start an engine that is port injected. One way of decreasing engine starting time of a port fueled engine is to inject fuel to engine cylinders when valves of the cylinders are open during an engine restart. However, injecting fuel during a time when an intake valves are open can reduce fuel vaporization and may cause fuel to impinge on cylinder walls, thereby increasing engine emissions.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for starting an engine, comprising: during an engine start and after an engine start request, selectively injecting fuel to a port of a single cylinder of the engine having an open intake valve at a time fuel is injected to the port; and injecting fuel to each remaining cylinder of the engine at a time when an intake valve of a cylinder receiving fuel is closed.
By injecting fuel to a single cylinder during intake valve opening of the cylinder, it may be possible to reduce engine emissions and improve engine starting. In particular, after the first cylinder is fueled at a time when its intake valve is open, fuel may be injected to remaining engine cylinders during timing when valves of the remaining cylinders are closed. Open valve injection to the one cylinder allows the cylinder to combust fuel earlier than if fuel injection started at only at closed valve timing. However, the cylinders that subsequently receive fuel can receive fuel when intake valves of the cylinders are closed so that fuel vaporization is improved and so that cylinder wall wetting may be decreased in the remaining cylinders at start. Thus, in one example, only one cylinder is fueled to promote early combustion while all remaining cylinders are fueled to reduce emissions and promote fuel vaporization.
In some examples, the open intake valve injection may be selectively applied. For example, during some conditions open intake valve injection may occur while during other conditions open intake valve injection is not permitted. Specifically, open intake valve injection is permitted when the intake valve opening duration from engine stop position to intake valve closing time (e.g. a remaining amount of intake valve opening duration) is greater than a predetermined number of crankshaft degrees. Selectively injecting fuel based on valve opening timing can reduce engine emissions by reducing the amount of excess fuel in the cylinder port for subsequent ignition events.
The present description may provide several advantages. Specifically, the approach may improve engine emissions by improving cylinder mixtures at engine start time. In addition, the approach may reduce engine noise during starting by helping to ensure that a desired amount of fuel is in a cylinder when combustion is initiated in the cylinder. Further, the approach may reduce excess fueling of engine cylinders during a start so as to reduce engine fuel consumption.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.